As the sun asserts itself more and more, anxious gardeners scan the skies, wondering if winter is really over and the growing season has truly begun. Old-timers may know by signs found in nature; but fortunately, there are other ways to make that determination. Knowing your region's plant hardiness zones, average temperatures, specific crop cultivation needs and how to harden off seedlings virtually ensures success in timing the best garden each year.
USDA Plant Hardiness Zones
The U.S. government maintains a website with information about average climate extremes, called the USDA Plant Hardiness Zone Map. Click on your state to see very specific color-coded information about your locale, including average low temperatures and the expected last day in the year your area experiences frost. A lot rides on that last date because many plants cannot tolerate freezing temperatures.
Sunset Magazine Zones
Garden discussion group members will often include their USDA zone number in their posts, and another number. What's this? Sunset Magazine maintains its own zone map by region, which offers descriptions of the types of plants that will thrive in each zone, as well as expected low temperatures. Many gardeners use both numbers to more accurately pinpoint the characteristics of their local climate.
Weather is Everything
Knowing your zone will tell you what the lowest temperature is likely to be, when the last frosty morning is apt to dawn, and even what kinds of plants grow well outside year-round. Still, it would be helpful to have an inkling of what the temperature range will be during a specific month. That's where weather sites like Intellicast and AccuWeather come in handy. The 10-day forecasts are nice, but what you really want to know are what the normal temperatures have been historically. On the AccuWeather site, type in your zip code, then click on the "Typical Weather" button at the bottom of the page to see normal ranges month by month or even day by day. On the Intellicast site, "Historic Averages" right near the top of the page for your region will yield the same information.
Now that you know as much as you can about what to expect outside, start reading those seed packets. Many of them provide instructions like: "Start indoors six weeks before last frost," or "Sow directly in soil that has warmed to 50 degrees Fahrenheit." For Zone 9, 14, the first sentence means that you can ring in the New Year starting seeds in pots because the likely last frost date is Feb. 15. March may be when the average soil temperature exceeds 50 F; scan the 10-day forecast to be sure before actually putting the seeds in the ground. Other instructions may mention that light frosts are okay for certain crops.
Even if the seed packet advised transplanting after six weeks or so, the seedlings have had it good in your nice, warm house. Going directly outdoors, even in temperatures they can withstand, will be a shock for them. To alleviate this somewhat, allow them limited exposure to the great outdoors. This gives them time to adjust. This more gradual transplanting method is known as "hardening off," and it's simply a matter of putting the transplants outside for longer and longer periods of time each day, over the course of a week or two.
No amount of information will fully insulate gardeners against those "freak, once-in-a-hundred-years" blizzards, but most weather follows a reasonably predictable pattern. Taking the time to be informed will likely ensure planting success.